The present disclosure relates to a magnetic one-component developing toner.
As dry developing methods currently practically employed in electrophotography, two-component development and magnetic one-component development are known. In the two-component development, a toner and a carrier are used. In the magnetic one-component development, a carrier is not used but a toner containing a magnetic powder is used. The toner containing a magnetic powder (hereinafter sometimes referred to as the magnetic toner) used in the magnetic one-component development has advantages of low cost and excellent durability. In such a magnetic toner, a polyester resin is often used as a binder resin because a coloring agent or a magnetic powder can be satisfactorily dispersed in the toner and the toner can easily attain excellent low-temperature fixability when the polyester resin is used as a binder resin.
If an image is formed by using a magnetic toner containing a polyester resin as a binder resin in a high-temperature and high-humidity environment, however, the image density of the formed image is liable to be lower than a desired value due to degradation of the charge amount of the toner.
In order to solve this problem, a particle powder of black magnetic iron oxide having an average particle size of 0.05 μm or more and 2.0 μm or less and an electrical resistance value of 1×108 Ω·cm or more under an applied voltage of 100 V has been proposed. If a magnetic toner containing such a particle powder of black magnetic iron oxide as a magnetic powder is used, an image can be formed in a desired image density even in a high-temperature and high-humidity environment.